Switching Criterion Research Articles

Universal Criterion and Phase Diagram for Switching a Magnetic Vortex Core in Soft Magnetic Nanodots

The universal criterion for ultrafast vortex-core switching between the up- and down-core bistates in soft magnetic nanodots is investigated by micromagnetic simulations along with vortex-core switching that occurs whenever the velocity of vortex-core motion reaches its critical velocity, upsilon cri = (1.66 +/- 0.18) gamma mean square root of Aex (e.g., upsilon cri = 330 +/- 37 m/s for Permalloy), with the exchange stiffness Aex and the gyromagnetic ratio gamma. On the basis of the universality of upsilon cri, phase diagrams for the vortex-core switching event and switching time with respect to both the amplitude and frequency of a circularly rotating magnetic field are calculated.

A phenomenological constitutive model for magnetostrictive materials and ferroelectric ceramics

AbstractThe contribution is concerned with a thermodynamic consistent constitutive model for magnetostrictive materials and ferroelectric ceramics. It captures the nonlinear phenomenological behavior which is described by hysteresis effects. Magnetostrictive alloys and ferroelectric ceramics belong to the multifunctional materials. In recent years these materials have become widely–used in actor and sensor applications. They characterize an inherent coupling between deformation and magnetic or electric field. Due to the similarities of the coupled differential equations a uniform approach is applied for both phenomena. The presented three–dimensional material model is thermodynamically motivated. It is based on the definition of a specific free energy function and a switching criterion. Furthermore an additive split of strain and the magnetic or electric field in a reversible and an irreversible part is suggested. The irreversible quantities serve as internal variables, which is analog to plasticity theory. A one–to–one–relation between the two internal variables provides conservation of volume for the irreversible strains. The presented material model can approximate the ferromagnetic or ferroelectric hysteresis curve and the related butterfly hysteresis. Furthermore an extended approach for ferrimagnetic behavior, which occurs in magnetostrictive materials, is presented. Some numerical simulations demonstrate the capability of the presented model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Combined switching and power control for diversity and multiplexing in MIMO systems with cochannel interference

Diversity and multiplexing can relax the throughput limitations caused by the interference and the frequency-selective fading channel, respectively. An algorithm that uses the throughput as the selection criterion for switching between diversity and multiplexing is thus proposed in this paper. Owing to the throughput-based switching, the proposed algorithm can always get the largest throughput between diversity and multiplexing. In addition, the power control procedures for diversity and multiplexing are also proposed to further enhance the throughput.

A constitutive model for magnetostrictive and piezoelectric materials

This paper is concerned with a macroscopic nonlinear constitutive law for magnetostrictive alloys and ferroelectric ceramics. It accounts for the hysteresis effects which occur in the considered class of materials. The uniaxial model is thermodynamically motivated and based on the definition of a specific free energy function and a switching criterion. Furthermore, an additive split of the strains and the magnetic or electric field strength into a reversible and an irreversible part is suggested. Analog to plasticity, the irreversible quantities serve as internal variables. A one-to-one-relation between the two internal variables provides conservation of volume for the irreversible strains. The material model is able to approximate the ferromagnetic or ferroelectric hysteresis curves and the related butterfly hysteresis curves. Furthermore, an extended approach for ferrimagnetic behavior which occurs in magnetostrictive materials is presented. A main aspect of the constitutive model is its numerical treatment. The finite element method is employed to solve the coupled field problem. Here the usage of the irreversible field strength permits the application of algorithms of computational inelasticity. The algorithmic consistent tangent moduli are developed in closed form. Hence, quadratic convergence in the iterative solution scheme of governing balance equations is obtained.

Nonlinear constitutive behavior of ferroelectric materials

The ferroelectric specimen is considered as an aggregation of many randomly oriented domains. According to this mechanism, a multi-domain mechanical model is developed in this paper. Each domain is represented by one element. The applied stress and electric field are taken to be the stress and electric field in the formula of the driving force of domain switching for each element in the specimen. It means that the macroscopic switching criterion is used for calculating the volume fraction of domain switching for each element. By using the hardening relation between the driving force of domain switching and the volume fraction of domain switching calibrated, the volume fraction of domain switching for each element is calculated. Substituting the stress and electric field and the volume fraction of domain switching into the constitutive equation of ferroelectric material, one can easily get the strain and electric displacement for each element. The macroscopic behavior of the ferroelectric specimen is then directly calculated by volume averaging. Meanwhile, the nonlinear finite element analysis for the ferroelectric specimen is carried out. In the finite element simulation, the volume fraction of domain switching for each element is calculated by using the same method mentioned above. The interaction between different elements is taken into account in the finite element simulation and the local stress and electric field for each element is obtained. The macroscopic behavior of the specimen is then calculated by volume averaging. The computation results involve the electric butterfly shaped curves of axial strain versus the axial electric field and the hysteresis loops of electric displacement versus the electric field for ferroelectric specimens under the uniaxial coupled stress and electric field loading. The present theoretical prediction agrees reasonably with the experimental results.

A Switching Criterion for Intensification and Diversification in Local Search for SAT12

We propose a new switching criterion, namely the evenness or unevenness of the distribution of variable weights, and use this criterion to combine intensification and diversification in local search for SAT. We refer to the ways in which state-of-the-art local search algorithms adaptG2 W SATP and V W select a variable to flip, as heuristic adaptG2 W SATP and heuristic V W , respectively. To evaluate the effectiveness of this criterion, we apply it to heuristic adaptG2 W SATP and heuristic V W , in which the former intensifies the search better than the latter, and the latter diversifies the search better than the former. The resulting local search algorithm, which switches between heuristic adaptG2 W SATP and heuristic V W in every step according to this criterion, is called Hybrid. Our experimental results show that, on a broad range of SAT instances presented in this paper, Hybrid inherits the strengths of adaptG2 W SATP and V W , and exhibits generally better performance than adaptG2 W SATP and V W . In addition, Hybrid compares favorably with state-of-the-art local search algorithm R+adaptNovelty+ on these instances. Furthermore, without any manual tuning parameters, Hybrid solves each of these instances in a reasonable time, while adaptG2 W SATP , V W , and R+adaptNovelty+ have difficulty on some of these instances.

무충돌 전환 구현 알고리즘을 사용한 전비행영역 제어기 교체법

이 논문에서는 최근에 개발한 무충돌 전환 구현 알고리즘을 사용하여 전비행영역 제어를 위한 제어기 교체법을 제시한다. 이 교체법은 비행기의 속도와 고도에 따라 제어기를 교체하는 일반적인 방법과 제어기 교체 기준으로 충돌 현상에 관계된 가격함수를 사용하는 최적화 방법을 적절한 규칙에 의해 결합한 것이다. 제안된 제어기 교체법의 성능을 확인하기 위해 시험표준 문제로 고성능 비행체에 적용하여 넓은 비행영역에서 모의실험을 수행하고 제어성능이 향상됨을 예시한다. This paper has proposed a controller switching scheme for full-envelope aircraft control using the bumpless transfer implementation algorithm developed recently. This switching scheme has combined by proper rules the common existing method which switches the controller according to attitude and mach number of the aircraft with an optimization method which uses the cost function relating to bump phenomenon by means of controller switching criterion. This paper exemplifies the control performance improvement via simulations applied to a high performance aircraft benchmark problem in a wide operating range to test the proposed controller switching scheme.

Nonlinear finite element modeling of polycrystalline ferroelectrics based on constrained domain switching

A review of the nonlinear finite element formulations for ferroelectrics shows that instability related to domain switching may arise in formulations using a phenomenological constitutive model or micromechanical domain switching criterion. To overcome the instability problems and to predict the experimentally observed incomplete non-180° switching in ferroelectrics, a constrained domain switching model for polycrystalline ferroelectrics is proposed in this paper and implemented in a finite element code. In the proposed model, a ferroelectric polycrystalline is made up of numerous random oriented grains, each of which contains multi-domains and is represented by a finite element. Charge screening effect in real ferroelectrics is also taken into account in the model, thus 180° domain switching is not constrained. While the internal stress induced by non-180° switching cannot be compensated in a similar manner and is considered naturally by the finite element method. The fraction of non-180° switching in each grain is obtained through a dichotomy approximation. Selected numerical results show that during electrical poling, 180° switching is usually complete while 90° switching is only about 2% for both BaTiO 3 and tetragonal PZT ceramics, which agree well with the experimental results.

Robust switching blind equalizer for wireless cognitive receivers

Kurtosis minimization has been applied for the existing blind equalization schemes but the corresponding optimization procedures are very sensitive to the channel conditions and the initial conditions. In this paper, we introduce a new cognitive receiver front-end, which includes a novel switching blind equalizer and an automatic modulation classifier. We design a switching criterion based on the kurtosis/normalized moment ratio threshold to select the better signal between the raw data and the equalized sequence. Simulations demonstrate that our proposed robust switching blind equalization scheme can significantly outperform the existing blind equalizer and would not degrade the subsequent modulation classification accuracy.

Energy principle and nonlinear electric–mechanical behavior of ferroelectric ceramics

Many experimental observations have shown that a single domain in a ferroelectric material switches by progressive movement of domain walls, driven by a combination of electric field and stress. The mechanism of the domain switch involves the following steps: initially, the domain has a uniform spontaneous polarization; new domains with the reverse polarization direction nucleate, mainly at the surface, and grow though the crystal thickness; the new domain expands sideways as a new domain continues to form; finally, the domain switch coalesces to complete the polarization reversal. According to this mechanism, the volume fraction of the domain switching is introduced in the constitutive law of the ferroelectric material and used to study the nonlinear constitutive behavior of a ferroelectric body in this paper. The principle of stationary total potential energy is put forward in which the basic unknown quantities are the displacement u i , electric displacement D i and volume fraction ρ I of the domain switching for the variant I. The mechanical field equation and a new domain switching criterion are obtained from the principle of stationary total potential energy. The domain switching criterion proposed in this paper is an expansion and development of the energy criterion established by Hwang et al. [1]. Based on the domain switching criterion, a set of linear algebraic equations for determining the volume fraction ρ I of domain switching is obtained, in which the coefficients of the linear algebraic equations only contain the unknown strain and electric fields. If the volume fraction ρ I of domain switching for each domain is prescribed, the unknown displacement and electric potential can be obtained based on the conventional finite element procedure. It is assumed that a domain switches if the reduction in potential energy exceeds a critical energy barrier. According to the experimental results, the energy barrier will strengthen when the volume fraction of the domain switching increases. The external mechanical and electric loads are increased step by step. The volume fraction ρ I of domain switching for each element obtained from the last loading step is used as input to the constitutive equations. Then the strain and electric fields are calculated based on the conventional finite element procedure. The finite element analysis is carried out on the specimens subjected to uniaxial coupling stress and electric field. Numerical results and available experimental data are compared and discussed. The present theoretic prediction agrees reasonably with the experimental results.

A New Weak Fault Component Reactance Distance Relay Based on Voltage Amplitude Comparison

A new weak fault component reactance distance relay is proposed in this paper. By adaptive setting of the compensated voltage, the scheme synthesizes the performance of the impedance distance relay and the reactance distance relay. The distance protection relay on the receiving end will misoperate when the fault resistance is larger than the critical resistance. So a new switching criterion is applied to eliminate this disadvantage. Based on that, the proposed scheme can detect the fault with the high fault resistance in the setting coverage, regardless of whether the relay is located at the receiving end or the sending end. Test results from the simulation and experimental conditions show that the new scheme is successful in detecting the internal fault. It has higher sensitivity and selectivity during different conditions than the traditional fault component protection schemes.

Fault-Tolerant Switching Scheme with Multiple Sensor-Controller Pairs

This paper deals with the problem of achieving high performance and fault tolerance properties of a given plant by switching between a collection of different sensor-controller pairs. We assume that each sensor-controller pair has been previously designed to achieve an appropriate performance objective according to disturbances, sensor noises, available bandwidth and uncertainties. The proposed strategy selects, at each instant of time, the sensor-controller pair that minimises a suitable switching criterion. Stability of the switching system under normal (fault-free) operation conditions is established in the main result of this paper. In addition, a simulation example of active suspension control illustrates that the proposed switching system is able to maintain performance levels, and to preserve stability under the occurrence of severe faults in some of the sensors.

Ferroelectrics: experiments, micromechanics, and constitutive modeling

In this paper, we will first discuss the typical hysteresis properties observed with ferroelectric materials in relation to the underlying domain switching processes. Then, we will present an experimental investigation determining the critical states of combined coaxial electrical and mechanical loading needed to initiate domain switching processes (switching criterion). Next, we will present a micromechanical finite element simulation of a ferroelectric volume element, where each grain exhibits single crystal behavior for the switching of its domains. Finally, we will introduce a micromechanically based constitutive model, which relies on internal variables representing an approximate distribution orientation function of the micro-dipoles. This constitutive model allows for the finite element analysis of the poling process of piezoceramic devices.

A Monolithic Buck Converter With Near-Optimum Reference Tracking Response Using Adaptive-Output-Feedback

A monolithic output-ripple-based buck converter with adaptive output and ultra-fast reference tracking is presented. Fixed-switching-frequency V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -control is used in steady-state operation; while its speed limitation during reference tracking is eliminated by employing end-point prediction, a novel oscillator with clock-holding function, and the proposed adaptive-output-feedback (AOFB)-scheme. The AOFB-scheme is obtained from a detailed analysis of the dynamics of general output-ripple-based controller during reference tracking. Then, an adaptive feedback voltage which satisfies the switching criterion for optimum switch control in reference tracking is formulated, and is incorporated into the controller design. The resultant single ON/OFF-switching during reference tracking is very close to the optimal solution for fast reference tracking. Moreover, it also leads to the lowest switching loss and minimized conduction loss at the fastest tracking speed, making the converter very suitable for adaptive-output applications. Fabricated in a 0.35 mum CMOS process, the 3-V input prototype chip exhibits stable operation across a wide output range of 0.7-2.4 V. High tracking speed within 10 mus/V is measured with different output voltages and output voltage steps. Maximum efficiency of 96% is obtained at 260 mA output current, while maximum output current is 800 mA.

Energy principle of ferroelectric ceramics and single domain mechanical model

Many physical experiments have shown that the domain switching in a ferroelectric material is a complicated evolution process of the domain wall with the variation of stress and electric field. According to this mechanism, the volume fraction of the domain switching is introduced in the constitutive law of ferroelectric ceramic and used to study the nonlinear constitutive behavior of ferroelectric body in this paper. The principle of stationary total energy is put forward in which the basic unknown quantities are the displacement u i , electric displacement D i and volume fraction ρ I of the domain switching for the variant I. Mechanical field equation and a new domain switching criterion are obtained from the principle of stationary total energy. The domain switching criterion proposed in this paper is an expansion and development of the energy criterion. On the basis of the domain switching criterion, a set of linear algebraic equations for the volume fraction ρ I of domain switching is obtained, in which the coefficients of the linear algebraic equations only contain the unknown strain and electric fields. Then a single domain mechanical model is proposed in this paper. The poled ferroelectric specimen is considered as a transversely isotropic single domain. By using the partial experimental results, the hardening relation between the driving force of domain switching and the volume fraction of domain switching can be calibrated. Then the electromechanical response can be calculated on the basis of the calibrated hardening relation. The results involve the electric butterfly shaped curves of axial strain versus axial electric field, the hysteresis loops of electric displacement versus electric filed and the evolution process of the domain switching in the ferroelectric specimens under uniaxial coupled stress and electric field loading. The present theoretic prediction agrees reasonably with the experimental results given by Lynch.

Electromagnetic optimisation using sensitivity analysis in the frequency domain

Gradient-based optimisation relies on the response Jacobian whose evaluation constitutes a major computational overhead in full-wave numerical analysis. Adjoint-based techniques may offer numerically efficient solutions, but their implementation is too involved in the case of full-wave computations. A simple approach that uses the self-adjoint sensitivity analysis and Broyden&apos;s update is proposed. The overhead of the Jacobian computation is greatly reduced because an adjoint system analysis is not needed and because Broyden&apos;s update is used to compute the system matrix derivatives. To improve the robustness of the Broyden update in the sensitivity analysis, we propose a switching criterion between the Broyden and the finite-difference estimation of the system matrix derivatives. We illustrate and validate the proposed method using full-wave commercial electromagnetic solvers based on the finite-element method as well as on the method of moments. Different gradient-based optimisation algorithms are exploited in the examples where efficiency is compared in terms of CPU time savings.

Computer simulation of carbon nanotube pull-out from polymer by the molecular dynamics method

Abstract The influence of the polymer matrix density, chemical cross-links in the interface, and geometrical defect in the carbon nanotubes (CNTs) on the CNT pull-out from polymer has been analyzed by the molecular dynamics simulation. The interfacial shear strength (ISS) has also been estimated with the change of total potential energy. In the simulation, the crystalline polyethylene matrix is set up in a hexagonal array with the polymer chains parallel to the CNT axis. First, we investigate the effect of the polymer matrix density on the ISS by changing the distance between the chains. Simulated results show that the ISS increases with the increase of matrix density. Next, we examine the cross-link effect on the ISS by adding polyethylene cross-links in the interface. Here, an energy based switching criterion addressing cross-links traveling on the CNT has been proposed. It is found that the presence of cross-links and the cross-link positions affect the ISS. Finally, pentagon–heptagon defect, which reduces the tensile strength of the CNT and has been experimentally observed by Hashimoto et al. [Hashimoto A, Suenaga K, Gloter A, Urita K, Iijima S. Direct evidence for atomic defects in graphene layers. Nature 2004;430:870–3], has been addressed as a geometrical defect in the CNT. When cross-links are present between the CNT and the polymer, this defect reduces the ISS due to the improper connections of cross-links around this defective region.

A simplified mesh‐free method for shear bands with cohesive surfaces

AbstractA simple methodology to model shear bands as strong displacement discontinuities in a mesh‐free particle method is presented. The shear band is represented as a set of sheared particles. A sheared particle is developed through enrichment by tangential displacement discontinuities. The representation of the shear band as set of cohesive segments provides a simple and versatile model of shear bands. The loss of material stability is used as the criterion for switching from a classical continuum description of the constitutive behaviour to a traction‐separation law acting on the discontinuity surface. The method is implemented for two and three dimensions. Examples of shear band progression in rate‐dependent and rate‐independent materials are presented, including the Kalthoff problem, where the transition from brittle fracture to shear banding is studied. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Domain switching anisotropy in poled lead titanate zirconate ceramics under orthogonal electromechanical loading

Domain switching process in aged lead titanate zirconate ceramics after hyper-TC (TC is the Curie temperature) poling was studied under two types of orthogonal electromechanical loading: (i) axial electric field E3 coupled with lateral compression stresses σ11 and (ii) axial compression stresses σ33 coupled with lateral electric fields E1. It is found that in the lateral direction, both the coercive field and the switchable polarization are significantly smaller than that in the original poling direction and that the lateral coercive field does not decrease but increase with the increasing axial compression, which contradicts with the widely accepted domain switching criterion by Hwang et al. [Acta. Metall. Mater. 43, 2073 (1995)]. The alignment of defect dipoles during aging, together with its effect on domain switching, is employed to explain the observed domain switching anisotropy. Furthermore, the domain stabilizing effect of aligned defect dipoles may lead to a design of large electrostriction actuators.

Markov-switching model selection using Kullback–Leibler divergence

In Markov-switching regression models, we use Kullback-Leibler (KL) divergence between the true and candidate models to select the number of states and variables simultaneously. In applying Akaike information criterion (AIC), which is an estimate of KL divergence, we find that AIC retains too many states and variables in the model. Hence, we derive a new information criterion, Markov switching criterion (MSC), which yields a marked improvement in state determination and variable selection because it imposes an approriate penalty to mitigate the over-retention of states in the Markov chain. MSC performs well in Monte Carlo studies with single and multiple states, small and large samples, and low and high noise. Furthermore, it not only applies to Markov-switching regression models, but also performs well in Markov-switching autoregression models. Finally, the usefulness of MSC is illustrated via applications to the U.S. business cycle and the effectiveness of media advertising.